Modification of 193 nm sensitive photoresist materials by electron beam exposure

ABSTRACT

A process for increasing the etch resistance of photoresists, especially positive working 193 nm sensitive photoresists which are suitable for use in the production of microelectronic devices such as integrated circuits. A 193 nm photosensitive composition is coated onto a substrate, exposed to activating energy at a wavelength of 193 nm to decompose the polymer in the imagewise exposed areas; and developed to remove the exposed nonimage areas. Then the image areas are exposed to sufficient electron beam radiation to increase the resistance of the image areas to an etchant.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for increasing the etchresistance of photoresists which are suitable for use in the productionof microelectronic devices such as integrated circuits. Moreparticularly, the invention provides a process for increasing the etchresistance of positive working 193 nm sensitive photoresists.

2. Description of the Related Art

The production of positive photoresists is well known in the art asexemplified by U.S. Pat. Nos. 3,666,473; 4,115,128 and 4,173,470. Thesecontain aqueous alkali soluble polyvinyl phenol or phenol formaldehydenovolak resins together with light sensitive materials, usually asubstituted naphthoquinone diazide compound. The resins and sensitizersare dissolved in an organic solvent and are applied as a thin filmcoating to a substrate suitable for the particular application desired.The resin component of photoresist formulations is soluble in an aqueousalkaline solution, but the photosensitizer is not. Upon imagewiseexposure of the coated substrate to actinic radiation, the exposed areasof the coating are rendered more soluble than the unexposed areas. Thisdifference in solubility rates causes the exposed areas of thephotoresist coating to be dissolved when the substrate is immersed in analkaline developing solution, while the unexposed areas aresubstantially unaffected, thus producing a positive image on thesubstrate. The uncovered substrate is thereafter subjected to an etchingprocess. Frequently, this involves a plasma etching against which theresist coating must be sufficiently stable. The photoresist coatingprotects the covered areas of the substrate from the etchant and thusthe etchant is only able to etch the uncovered areas of the substrate.Thus, a pattern can be created on the substrate which corresponds to thepattern of the mask or template that was used to create selectiveexposure patterns on the coated substrate prior to development.

Photoresists are either positive working or negative working. In anegative working resist composition, the imagewise light struck areasharden and form the image areas of the resist after removal of theunexposed areas with a developer. In a positive working resist theexposed areas are the non-image areas. The light struck parts arerendered soluble in aqueous alkali developers. The ability to reproducevery small dimensions, is extremely important in the production of largescale integrated circuits on silicon chips and similar components. Asthe integration degree of semiconductor devices becomes higher, finerphotoresist film patterns are required. One way to increase circuitdensity on such a chip is by increasing the resolution capabilities ofthe resist. Positive photoresists have been found to be capable of muchhigher resolution and have almost universally replaced negative resistsfor this purpose.

The optimally obtainable microlithographic resolution is essentiallydetermined by the radiation wavelengths used for the selectiveirradiation. However the resolution capacity that can be obtained withconventional deep UV microlithography has its limits. In order to beable to sufficiently resolve optically small structural elements,wavelengths shorter than deep UV radiation must be utilized. The use ofUV radiation has been employed for many applications, particularlyradiation with a wavelength of 193 nm. In particular, the radiation ofargon fluoride excimer lasers, which has a wavelength of 193 nm isuseful for this purpose. The deep UV photoresist materials that are usedtoday, however, are not suitable for 193 nm exposure. Materials based onphenolic resins as a binding agent, particularly novolak resins orpolyhydroxystyrene derivatives have too high an absorption atwavelengths below 200 nm and one cannot image through films of thenecessary thickness. This high absorption at 193 nm radiation results inside walls of the developed resist structures which do not form thedesired vertical profiles. Rather they have an oblique angle with thesubstrate which causes poor optical resolution characteristics at theseshort wavelengths. Polyhydroxystyrene based resists can be used in topsurface imaging applications in which a very thin (˜500 Å) layer ofresist is required to be transparent at the ArF wavelength. Thisinvention involves the use of 193 nm resists in single layer processes.

Chemical amplification resist films have been developed, which have beenfound to have superior resolution. 193 nm photoresists are based onchemically amplified deprotection. With this mechanism, a molecule ofphotogenerated acid catalyzes the breaking of bonds in a protectinggroup of a polymer. During the deprotecting process, another molecule ofthe same acid is created as a byproduct, and continues theacid-catalytic deprotection cycle. The chemistry of a 193 nm photoresistis based on polymers such as, but not limited to, acrylates, cyclicolefins with alicyclic groups, and hybrids of the aforementionedpolymers which lack aromatic rings, which contribute to opacity at 193nm. It has thus been known to utilize photoresists based on methacrylateresins for the production of microstructures by means of 193 nmradiation.

However, chemically amplified resist films have not played a significantrole in the fine pattern process using deep UV because they lacksufficient etch resistance, thermal stability, post exposure delaystability and processing latitude. While such photoresists aresufficiently transparent for 193 nm radiation, they do not have theetching stability customary for resists based on phenolic resins forplasma etching. A typical chemical amplification photoresist filmcomprises a polymer, a photoacid generator, and other optionaladditives. The polymer is required to be soluble in the chosen developersolution, and have high thermal stability and low absorbance to the 193nm exposure wavelength in addition to having excellent etch resistance.Since resists containing aromatic compounds show high absorbance to ArF(193 nm) while non-aromatic matrix resins have a poor etch resistance,these contrasting weak points are factors retarding the development ofexcellent photoresist films for ArF lithography. It would be desirableto overcome the above mentioned problems and to provide a photoresistfilm superior in etch resistance, as well as transmittance to deep UV.

There have been several attempts to solve this problem. One attempt toimprove the etching stability of photoresists based on meth(acrylate)introduced cycloaliphatic groups into the meth(acrylate) polymers. Thisleads to an improvement in etching stability, but not to the desiredextent. Another proposal aims at producing sufficient etching stabilityonly after irradiation in the resist coating. It has been proposed totreat the substrate with the finished, developed, image-structuredphotoresist coating with specific alkyl compounds of magnesium oraluminum, in order to introduce the given metals in the resist materialas etching barriers (See U.S. Pat. No. 4,690,838). The use ofmetal-containing reagents, however, is generally not desired inmicrolithography process, due to the danger associated withcontamination of the substrate with metal ions.

It has now been found according to the present invention, that bysubjecting a developed photoresist to electron beam irradiation, aresist image is produced which is still sufficiently transparent forradiation with a wavelength of approximately 193 nm and which is nowsufficiently stable to permit plasma etching. In this way, it ispossible to produce a photoresist which can be exposed at approximately193 nm wavelength, which also has an etching rate that is comparable toconventional resists based on phenolic resin, without needing to treatthe resist coating with metal compounds in order to increase the etchingstability. The present invention therefore provides a process forincreasing the etch stability of photoresist compositions which aretransparent at a wavelength of approximately 193 nm.

SUMMARY OF THE INVENTION

The invention provides a process for producing an etch resistant imagewhich comprises:

(a) coating and drying a photosensitive composition onto a substrate,which photosensitive composition comprises

(i) at least one water insoluble, acid decomposable polymer which issubstantially transparent to ultraviolet radiation at a wavelength ofabout 193 nm, wherein said polymer is present in the photosensitivecomposition in an amount sufficient to form a uniform film of thecomposition components when it is coated on a substrate and dried;

(ii) at least one photosensitive compound capable of generating an acidupon exposure to sufficient activating energy at a wavelength of about193 nm, said photosensitive compound being present in an amountsufficient to substantially uniformly photosensitize the photosensitivecomposition;

(b) imagewise exposing the photosensitive composition to sufficientactivating energy at a wavelength of 193 nm to cause the photosensitivecompound to generate sufficient acid to decompose the polymer in theimagewise exposed areas of the photosensitive composition;

(c) developing the photosensitive composition to thereby remove theexposed nonimage areas and leaving the unexposed image areas of thephotosensitive composition;

(d) irradiating the image areas of the photosensitive composition tosufficient electron beam radiation to thereby increase the resistance ofthe photosensitive composition in the image areas to an etchant.

The invention also provides a process for producing a microelectronicdevice image which comprises:

(a) coating and drying a photosensitive composition onto a semiconductorsubstrate, which photosensitive composition comprises

(i) at least one water insoluble, acid decomposable polymer which issubstantially transparent to ultraviolet radiation at a wavelength ofabout 193 nm, wherein said polymer is present in the photosensitivecomposition in an amount sufficient to form a uniform film of thecomposition components when it is coated on a substrate and dried;

(ii) at least one photosensitive compound capable of generating an acidupon exposure to sufficient activating energy at a wavelength of about193 nm, said photosensitive compound being present in an amountsufficient to substantially uniformly photosensitize the photosensitivecomposition;

(b) imagewise exposing the photosensitive composition to sufficientactivating energy at a wavelength of 193 nm to cause the photosensitivecompound to generate sufficient acid to decompose the polymer in theimagewise exposed areas of the photosensitive composition;

(c) developing the photosensitive composition to thereby remove theexposed nonimage areas and leaving the unexposed image areas of thephotosensitive composition;

(d) irradiating the image areas of the photosensitive composition tosufficient electron beam radiation to thereby increase the resistance ofthe photosensitive composition in the image areas to an etchant.

The invention further provides a microelectronic device image producedby a process which comprises:

(a) coating and drying a photosensitive composition onto a semiconductorsubstrate, which photosensitive composition comprises

(i) at least one water insoluble, acid decomposable polymer which issubstantially transparent to ultraviolet radiation at a wavelength ofabout 193 nm, wherein said polymer is present in the photosensitivecomposition in an amount sufficient to form a uniform film of thecomposition components when it is coated on a substrate and dried;

(ii) at least one photosensitive compound capable of generating an acidupon exposure to sufficient activating energy at a wavelength of about193 nm, said photosensitive compound being present in an amountsufficient to substantially uniformly photosensitive the photosensitivecomposition; p1 (b) imagewise exposing the photosensitive composition tosufficient activating energy at a wavelength of 193 nm to cause thephotosensitive compound to generate sufficient acid to decompose thepolymer in the imagewise exposed areas of the photosensitivecomposition;

(c) developing the photosensitive composition to thereby remove theexposed nonimage areas and leaving the unexposed image areas of thephotosensitive composition;

(d) irradiating the image areas of the photosensitive composition tosufficient electron beam radiation to thereby increase the resistance ofthe photosensitive composition in the image areas to an etchant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a graph comparing etch rates for two 193 nm resists and a248 nm resist.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The first step of the process according to the invention is coating anddrying a photosensitive composition onto a substrate. The photosensitivecompositions useful for the invention are themselves well known in theart and are composed of a mixture of a water insoluble, aciddecomposable polymer which is substantially transparent to ultravioletradiation at a wavelength of about 193 nm, a photosensitive compoundcapable of generating an acid upon exposure to sufficient activatingenergy at a wavelength of about 193 nm, and optional other ingredients.

Suitable substrates nonexclusively include silicon, aluminum, lithiumniobate, polymeric resins, silicon dioxide, doped silicon dioxide,gallium arsenide, Group III/V compounds, silicon nitride, tantalum,copper, polysilicon, ceramics and aluminum/copper mixtures.Semiconductor substrates are most preferred. Lines may optionally be onthe substrate surface. The lines, when present, are typically formed bywell known lithographic techniques and may be composed of a metal, anoxide, a nitride or an oxynitride. Suitable materials for the linesinclude silica, silicon nitride, titanium nitride, tantalum nitride,aluminum, aluminum alloys, copper, copper alloys, tantalum, tungsten andsilicon oxynitride. These lines form the conductors or insulators of anintegrated circuit. Such are typically closely separated from oneanother at distances preferably of from about 20 micrometers or less,more preferably from about 1 micrometer or less, and most preferably offrom about 0.05 to about 1 micrometer.

Acid decomposable polymers suitable for a chemical amplification resistfilm for ArF laser exposure which are substantially transparent at 193nm are well known in the art and nonexclusively include cyclic olefins,and acrylics and methacrylates such as polyalkylacrylates andpolyalkylmethacrylates, norbornene containing polymers, and alicyclicpolymers. Cyclic olefin materials offer superior etch resistance,surpassing even that of novolac materials. The most widely employedroute involves free radical copolymerization of maleic anhydride with acyclic olefin monomer. The maleic anhydride serves as an oxygen-richpolar unit whose hydrophilic nature offsets the hydrophobic nature ofthe cyclic olefin monomer. Others polymers include polymethylacrylateand polymethylmethacrylate (PMMA) as well as copolymers thereof andpolymers which have a backbone of polymethylmethacrylate having pendantgroups which do not substantially reduce the transparency of the polymerat 193 nm. PMMA has a particularly high transmittance to the light of193 nm wavelength and it is known for its clarity, surface hardness, UVtransparency and chemical resistance PMMA is readily commerciallyavailable from Aldrich Chemical Company of Milwaukee, Wis. Preferablythe polymer has a molecular weight in the range of from about 1,000 toabout 800,000. Alicyclic polymers include acrylate/alicyclic polymerssuch as hybrid polymers produced by the free radical copolymerization ofnorbornene, maleic anhydride and either acrylic acid or t-butylacrylate. A terpolymer of acrylonitrile, tertiary-butyl methacrylate andmethacrylic acid has also been shown to have high transparency at 193 nmand excellent dry etch resistance.

Useful photosensitive compounds capable of generating an acid uponexposure to sufficient activating energy at a wavelength of about 193 nminclude onium salts such as sulfonium, diazonium and iodonium salts.Sulfonium salts are described in U.S. Pat. No. 4,537,854; diazoniumsalts are described in Light Sensitive Systems, Kosar, J.; John Wiley &Sons, New York, 1965. Iodonium salts are described in U.S. Pat. No.4,603,101.

The light sensitive composition may be formed by admixing theingredients in a suitable solvent composition. In the preferredembodiment the polymer is preferably present in the overall compositionin an amount of from about 50% to about 99% based on the weight of thesolid, i.e. non-solvent parts of the composition. A more preferred rangeof copolymer would be from about 80% to about 99% and most preferablyfrom about 82% to about 95% by weight of the solid composition parts.The photosensitive compound is preferably present in an amount rangingfrom about 1% to about 20% based on the weight of the solid, i.e.,non-solvent parts of the composition. A more preferred range of thephotosensitive compound would be from about 5% to about 20% by weight ofthe solid composition parts. In preparing the composition, the polymerand photosensitive compound are mixed with a sufficient amount of asolvent composition to form a uniform solution. Such solvents includepropylene glycol alkyl ether acetate, butyl acetate, ethylene glycolmonoethyl ether acetate, diglyme, cyclopentanone and propylene glycolmethyl ether acetate, among others. The composition may additionallycontain additives such as colorants, dyes, antistriation agents,leveling agents, crosslinkers, plasticizers, adhesion promoters, speedenhancers, solvents, acid generators, dissolution inhibitors andnon-ionic surfactants.

Examples of dye additives that may be used together with the photoresistcompositions of the present invention include Methyl Violet 2B (C.I. No.42535), Crystal Violet (C.I. 42555), Malachite Green (C.I. No. 42000),Victoria Blue B (C.I. No. 44045) and Neutral Red (C.I. No. 50040) in anamount of from about 1.0 to about 10.0 percent, based on the combinedweight of the solid parts of the composition. The dye additives helpprovide increased resolution by inhibiting back scattering of light offthe substrate. Anti-striation agents may be used up to five percentweight level, based on the combined weight of solids. Adhesion promoterswhich may be used include, for example,beta-(3,4-epoxy-cyclohexyl)ethyltrimethoxysilane;p-methyl-disilane-methyl methacrylate; vinyltrichlorosilane; andgamma-amino-propyl triethoxysilane up to a 4.0 percent based on thecombined weight of solids. Speed enhancers that may be used include, forexample, picric acid, nicotinic acid or nitrocinnamic acid at up to 20percent, based on the combined weight of copolymer and solids. Theseenhancers tend to increase the solubility of the photoresist coating inboth the exposed and unexposed areas, and thus they are used inapplications when speed of development is the overriding considerationeven though some degree of contrast may be sacrificed; i.e., while theexposed areas of the photoresist coating will be dissolved more quicklyby the developer, the speed enhancers will also cause a larger loss ofphotoresist coating from the unexposed areas. Non-ionic surfactants thatmay be used include, for example, nonylphenoxy poly(ethyleneoxy)ethanol;octylphenoxy(ethyleneoxy)ethanol; and dinonyl phenoxypoly(ethyleneoxy)ethanol at up to 10 percent based on the combinedweight of solids.

Photoresists which are photosensitive at 193 nm are well known in theart and widely commercially available, Such include K98 and D3 availablefrom the Shipley Company; 620-10 from Olin Microelectronics Materials,AM01, AM02 and AM03 from Japan Synthetic Rubber Company, TOK-TArF-5A-1and TOK-TArF-6A-1 from Tokyo Ohka Kogyo Co. Ltd, DUV-18L from BrewerScience. Other suitable photoresists include solutions ofpolymethylmethacrylate (PMMA), such as a liquid photoresist available as496 k PMMA, from OLIN HUNT/OCG, West Paterson, N.J. 07424, comprisingpolymethylmethacrylate with molecular weight of 496,000 dissolved inchlorobenzene (9 wt %); P(A-MAA) (poly methyl methacrylate-methacrylicacid); PMMA/IP(MMA-MAA) polymethylmethacrylate/(poly methylmethacrylate-methacrylic acid).

In the production of the microelectronic device of the presentinvention, one coats and dries the foregoing photosensitive compositionon a suitable substrate. The prepared resist solution can be applied toa substrate by any conventional method used in the photoresist art,including dipping, spraying, whirling and spin coating. When spincoating, for example, the resist solution can be adjusted as to thepercentage of solids content in order to provide coating of the desiredthickness given the type of spinning equipment utilized and the amountof time allowed for the spinning process. In a preferred embodiment ofthe invention, the photoresist layer is formed by centrally applying aliquid photoresist composition to the upper surface on a rotating wheelat speeds ranging from about 500 to about 6000 rpm, preferably fromabout 1500 to about 4000 rpm, for about 5 to about 60 seconds,preferably from about 10 to about 30 seconds, in order to spread thecomposition evenly across the upper surface. The thickness of thephotoresist layer may vary depending on the amount of liquid photoresistcomposition that is applied, but typically the thickness may range fromabout 500 Å to about 50,000 Å, and preferably from about 2000 Å to about12000 Å. The amount of photoresist composition which is applied may varyfrom about 1 ml to about 10 ml, and preferably from about 2 ml to about8 ml depending on the size of the substrate.

After the resist composition solution is coated onto the substrate, thesubstrate is temperature treated at approximately 20° C. to 200° C. Thistemperature treatment is done in order to reduce and control theconcentration of residual solvents in the photoresist while not causingsubstantial thermal degradation of the photosensitizer. In general onedesires to minimize the concentration of solvents and thus thistemperature treatment is conducted until substantially all of thesolvents have evaporated and a thin coating of photoresist composition,on the order of a micron in thickness, remains on the substrate. In apreferred embodiment the temperature is conducted at from about 50° C.to about 150° C. A more preferred range is from about 70° C. to about90° C. This treatment is conducted until the rate of change of solventremoval becomes relatively insignificant. The temperature and timeselection depends on the resist properties desired by the user as wellas equipment used and commercially desired coating times. Commerciallyacceptable treatment times for hot plate treatment are those up to about3 minutes, more preferably up to about 1 minute. In one example, a 30second treatment at 90° C. is useful. Treatment times increase to about20 to about 40 minutes when conducted in a convection oven at thesetemperatures.

After deposition onto the substrate, the photoresist layer is imagewiseexposed, such as via an ArF laser or through a polysilicon etch mask toactinic radiation. This exposure renders the photoresist layer moresoluble after exposure than prior to exposure. When such a chemicalamplification resist is exposed to light, activated acid induces acatalytic chain reaction to a photoresist film organic polymer,generating a significant amount of protons. In the resist, protons bringa large change into the solubility of the resin. When the photoresistfilm is irradiated by a high energy beam, e.g. 193 nm, acid (H⁺) isgenerated, reacting with the polymer. Acid is again generated and reactswith unreacted polymer. The polymer is then dissolved in a developingsolution. In contrast, the polymer at the non-exposed region maintainsits structure which is insoluble to the developing solution. With such amechanism, a good profile pattern can be made on a wafer substrate. Theamount of actinic radiation used is an amount sufficient to render theexposed portions of the photoresist layer imagewise soluble in asuitable developer. Preferably, UV radiation is used in an amountsufficient to render the exposed portions of the photoresist layerimagewise soluble is a suitable developer. UV exposure doses preferablyrange from about 5 mJ/cm² to about 300 mJ/cm², more preferably fromabout 5 mJ/cm² to about 100 mJ/cm² and still more preferably from about10 mJ/cm² to about 30 mJ/cm².

Exposure is preferably via an ArF laser, i.e. at a wavelength of fromabout 193 nm. When an ArF laser is used for exposure, exposure dosespreferably ranges from about 1 mJ/cm² to about 10 mJ/cm², morepreferably from about 2 mJ/cm² to about 8 mJ/cm².

Preferably the process further comprises the step of heating theimagewise exposing the photosensitive composition prior to developing,such as by baking, for a sufficient time and temperature to increase therate at which the acid decomposes the polymer in the imagewise exposedareas of the photosensitive composition. This drives the acid reactionfor better image formation. Such a heat treatment may be conducted attemperatures of from about 50° C. to about 150° C., preferably fromabout 120° C. to about 150° C. for from about 30 seconds to about 2minutes.

The development step may be conducted by immersion in a suitabledeveloping solution. The solution is preferably agitated, for example,by nitrogen burst agitation. The substrates are allowed to remain in thedeveloper until all, or substantially all, of the resist coating hasdissolved from the irradiated areas. Typical examples of the aqueousalkaline solutions suitable as the developer include sodium hydroxide,tetramethylammonium hydroxide, or aqueous solutions of hydroxides ofmetals belonging to the Groups I and II of the periodic table such aspotassium hydroxide. Aqueous solution of organic bases free from metalions such as tetraalkylammonium hydroxide, for example,tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide(TEAH) and tetrabutylammonium hydroxide (TBAH). More preferably,tetramethylammonium hydroxide (TMAH) are preferred. Furthermore, ifdesired, the aqueous basic solution used as the developer mayadditionally contain any additives such as a surface active agent inorder to improve the resulting development effect. After removal of thecoated wafers from the developing solution, an optional, although notrequired, post-development heat treatment or bake may be employed toincrease the adhesion of the coating as well as resistance to etchingsolutions and other substances. The post-development heat treatment cancomprise the oven baking of the coating and substrate below thecoating's softening point.

The remaining photoresist layer is then overall exposed to sufficientelectron beam radiation to render the patterned image more resistant toan etchant such as oxygen plasma etchants and chlorine etchants. Theelectron beam irradiating is conducted with a uniform, large-area,overall electron beam exposure source which simultaneously exposessubstantially all of the image areas of the photosensitive compositionsimultaneously. Electron beam radiation may take place in any chamberhaving a means for providing electron beam radiation to substratesplaced therein. It is preferred that the electron beam exposing step isconducted with a wide, large beam of electron radiation from alarge-area electron beam source. Preferably, an electron beam chamber isused which provides a large area electron source. Suitable electron beamchambers are commercially available from Electron Vision, a unit ofAlliedSignal Inc., under the trade name “ElectronCure™”. The principlesof operation and performance characteristics of such device aredescribed in U.S. Pat. No. 5,003,178, the disclosure of which isincorporated herein by reference. The temperature of the electron beamexposure preferably ranges from about 20° C. to about 450° C., morepreferably from about 50° C. to about 400° C. The electron beam energyis preferably from about 0.5 to about 30 KeV, and more preferably fromabout 1 to about 12 KeV and most preferably from about 9 to about 9 KeV.The dose of electrons is from about 1 to about 500,000 μC/cm²,preferably from about 50 to about 50,000 μC/cm² and more preferably fromabout 50 to about 5,000 μC/cm². The gas ambient in the electron beamtool can be any of the following gases: nitrogen, oxygen, hydrogen,argon, xenon, helium, ammonia, silane, a blend of hydrogen and nitrogen,ammonia or any combination of these gases. The electron beam current ispreferably from about 1 to about 150 mA, and more preferably from about1 to about 20 mA. The electron beam irradiating is conducted while thesubstrate is under a vacuum maintained in the range of from about 10⁻⁵to about 10² torr. Preferably, the electron beam exposing step isconducted with a wide, large beam of electron beam radiation from auniform large-are electron beam source which simultaneously covers theentire substrate area, i.e. an area of from about 4 inches to about 256square inches. The end result of the electron beam treatment will bephotoresist layers which are less soluble after exposure than prior toexposure. The resist compositions of the present invention are resistantto acid-base etching solutions and provide effective protection for theunexposed resist-coated areas of the substrate.

The following nonlimiting examples serve to illustrate the invention.

EXAMPLE 1

A layer of 193 nm photoresist (Sumitomo PAR-101A4) was spin-coated ontoa blank silicon substrate. The spin coater was a benchtop Laurell model.The dispense volume was 3-4 ml. The resist was spread over the substratewith a slow spin, 1000 rpm for ˜10 seconds. Then the spin speed wasramped to 3000 rpm and remained at 3000 rpm for 20 seconds. Thephotoresist layer and substrate were softbaked at 120° C. for 60 secondson a hot plate to drive off most of the solvent. The film thicknessdecreased during the softbake as solvent was evolved. After the softbakethe thickness was about 7,000 Å with the coat and bake conditionsdescribed above. Each photoresist film was measured with a J. A. Woollamspectroscopic ellipsometer to obtain post-coat thickness and opticalconstants. A 9-pt map with a 1-inch edge exclusion was used for themeasurements. FTIR spectroscopy was also performed to obtain infraredspectra of each film before electron beam cure. Each substrate was thensubjected to an electron beam irradiation treatment in the ElectronCuretool made by the Electron Vision Group of Allied Signal. A uniform dosedistribution recipe was employed and doses ranged from 10-5,000 μC/cm².Each photoresist film was measured with a J. A. Woollam spectroscopicellipsometer to obtain post-cure thickness and optical constants. A 9-ptmap with a 1-inch edge exclusion was used for the measurements. FTIRspectroscopy was also performed to obtain infrared spectra of each filmafter electron beam cure. The thickness, optical constants, and infraredspectra of each film before cure were compared to those after cure todetermine the extent of film shrinkage and changes to the opticalconstants. Each photoresist film was then etched for 15 seconds in aplasma etching tool using a standard aluminum etch chemistry (BCl₃/Cl₂).Each photoresist film was measured with a J. A. Woollam spectroscopicellipsometer to obtain post-etch thickness and optical constants. A 9-ptmap with a 1-inch edge exclusion was used for the measurements. Thethickness of each film after cure were compared to those after etch todetermine the etch rate in a metal etch chemistry. A graph of the etchrates at various e-beam doses is shown in the FIG. 1 and Table 1. It canbe seen that etch rate decreases sharply as e-beam exposure doseincreases.

EXAMPLE 2

A layer of 193 nm photoresist (Shipley XP 7022) was spin-coated onto ablank silicon substrate. The spin coater was a benchtop Laurell model.The dispense volume was 3-4 ml. The resist was spread over the substratewith a slow spin, 1000 rpm for ˜10 seconds. Then the spin speed wasramped to 3000 rpm and remained at 3000 rpm for 20 seconds. Thephotoresist layer and substrate were softbaked at 140° C. for 60 secondson a hot plate to drive off most of the solvent. The film thicknessdecreased during the softbake as solvent was evolved. After the softbakethe thickness was about 6,000 Å with the coat and bake conditionsdescribed above. Each photoresist film was measured with a J. A. Woollamspectroscopic ellipsometer to obtain post-coat thickness and opticalconstants. A 9-pt map with a 1-inch edge exclusion was used for themeasurements. FTIR spectroscopy was also performed to obtain infraredspectra of each film before electron beam cure. Each substrate was thensubjected to an electron beam irradiation treatment in the ElectronCuretool made by the Electron Vision Group of Allied Signal. A uniform dosedistribution recipe was employed and doses ranged from 10-5,000 μC/cm².Each photoresist film was measured with a J. A. Woollam spectroscopicellipsometer to obtain post-cure thickness and optical constants. A 9-ptmap with a 1-inch edge exclusion was used for the measurements. FTIRspectroscopy was also performed to obtain infrared spectra of each filmafter electron beam cure. The thickness, optical constants, and infraredspectra of each film before cure were compared to those after cure todetermine the extent of film shrinkage and changes to the opticalconstants. Each photoresist film was then etched for 15 seconds in aplasma etching tool using a standard aluminum etch chemistry (BCl₃/Cl₂).Each photoresist film was measured with a J. A. Woollam spectroscopicellipsometer to obtain post-etch thickness and optical constants. A 9-ptmap with a 1-inch edge exclusion was used for the measurements. Thethickness of each film after cure were compared to those after etch todetermine the etch rate in a metal etch chemistry. Graphs of etch ratesare shown in the FIG. 1 and Table 1. It can be seen that etch ratedecreases sharply as e-beam exposure dose increases.

EXAMPLE 3 Comparative

A layer of a 248 nm photoresist (Japan Synthetic Rubber Co. KRFM20G) wasspin-coated onto a blank silicon substrate. The spin coater was abenchtop Laurell model. The dispense volume was 3-4 ml. The resist wasspread over the substrate with a slow spin, 1000 rpm for ˜10 seconds.Then the spin speed was ramped to 3000 rpm and remained at 3000 rpm for20 seconds. The photoresist layer and substrate were softbaked at 140°C. for 60 seconds on a hot plate to drive off most of the solvent. Thefilm thickness decreased during the softbake as solvent was evolved.After the softbake the thickness was about 7,000 Å with the coat andbake conditions described above. Each photoresist film was measured witha J. A. Woollam spectroscopic ellipsometer to obtain post-coat thicknessand optical constants. A 9-pt map with a 1-inch edge exclusion was usedfor the measurements. FTIR spectroscopy was also performed to obtaininfrared spectra of each film before electron beam cure. Each substratewas then subjected to an electron beam irradiation treatment in theElectronCure tool made by the Electron Vision Group of Allied Signal. Auniform dose distribution recipe was employed and doses ranged from10-5,000 μC/cm². Each photoresist film was measured with a J. A. Woollamspectroscopic ellipsometer to obtain post-cure thickness and opticalconstants. A 9-pt map with a 1-inch edge exclusion was used for themeasurements. FTIR spectroscopy was also performed to obtain infraredspectra of each film after electron beam cure. The thickness, opticalconstants, and infrared spectra of each film before cure were comparedto those after cure to determine the extent of film shrinkage andchanges to the optical constants. Each photoresist film was then etchedfor 15 seconds in a plasma etching tool using a standard aluminum etchchemistry (BCl₃/Cl₂). Each photoresist film was measured with a J. A.Woollam spectroscopic ellipsometer to obtain post-etch thickness andoptical constants. A 9-pt map with a 1-inch edge exclusion was used forthe measurements. The thickness of each film after cure were compared tothose after etch to determine the etch rate in a metal etch chemistry.Graphs of etch rates are shown in the FIG. 1 and Table 1. It can be seenthat etch rate differences are insignificant for an e-beam exposed 248nm resist.

TABLE 1 ETCH RATES Å/minute E-BEAM DOSE (μc/cm²) EXAMPLE 3 EXAMPLE 2EXAMPLE 1 10 4251 4760 4508 20 3793 50 3751 100 3841 4464 4380 200 3942500 3965 3436 2788 1000 2932 2128 2000 3802 5000 3526 2312 1612

EXAMPLE 4

A layer of 193 nm photoresist (e.g., Sumitomo PAR-101A4) is spin-coatedonto a substrate, such as a silicon substrate. This substrate has somesemiconductor structures already in it. The spin coater is a benchtopLaurell spinner. The dispense volume is 3-4 ml. The resist is spreadover the substrate with a slow spin, 700-1000 rpm for ˜10 seconds. Thenthe spin speed is ramped to 3000 rpm and remains there for 20-30seconds. The photoresist layer and substrate are softbaked at 120° C.for 60 seconds on a hot plate to drive off most of the solvent. The filmthickness decreases during the softbake as solvent is evolved. After thesoftbake the thickness is about 7,000 Å (with the coat and bakeconditions described above). The photoresist film is exposed to actinicradiation; in this case, radiation of 193 nm wavelength, by a 193 nmstepper such as ISI ArF Microstepper, SVGL 193 Micrascan or ASML PAS5500/900, with a numerical aperture of ˜0.6 and a typical exposure doseof 5-10 mJ/cm². This causes photoacid to be generated. The photoresistfilm undergoes a post-exposure bake at 120° C. for 60 seconds tothermally activate the deprotection reaction. The result is an ideallylarge differential dissolution between the exposed and unexposed areas.The photoresist film is developed in an industry-standard 2.38 wt %aqueous TMAH (tetramethylammonium hydroxide) developer solution. Theexposed areas are dissolved away (for a positive photoresist) and theunexposed areas are left, forming the desired resist pattern.Photoresist residue is removed from the substrate in an oxygen plasmade-scumming process. The substrate then undergoes the electron beamirradiation treatment in the ElectronCure tool made by the ElectronVision Group of Allied Signal. The electron beam process modifies thephotoresist film (perhaps initiates crosslinking) to make it morethermally stable and mechanically robust, in preparation for etchprocessing or ion implantation. FTIR analysis indicates crosslinking ofthe electron beam exposed surface.

While the present invention has been particularly shown and describedwith reference to preferred embodiments, it will be readily appreciatedby those of ordinary skill in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe invention. It is intended that the claims be interpreted to coverthe disclosed embodiment, those alternatives which have discussed above,and all equivalents thereto.

What is claimed is:
 1. A process for producing an etch resistant imagewhich comprises: (a) coating and drying a photosensitive compositiononto a substrate, which photosensitive composition comprises (i) atleast one water insoluble, acid decomposable polymer which issubstantially transparent to ultraviolet radiation at a wavelength ofabout 193 nm, wherein said polymer is present in the photosensitivecomposition in an amount sufficient to form a uniform film of thecomposition components when it is coated on a substrate and dried; (ii)at least one photosensitive compound capable of generating an acid uponexposure to sufficient activating energy at a wavelength of about 193nm, said photosensitive compound being present in an amount sufficientto substantially uniformly photosensitize the photosensitivecomposition; (b) imagewise exposing the photosensitive composition tosufficient activating energy at a wavelength of 193 nm to cause thephotosensitive compound to generate sufficient acid to decompose thepolymer in the imagewise exposed areas of the photosensitivecomposition; (c) developing the photosensitive composition to therebyremove the exposed nonimage areas and leaving the unexposed image areasof the photosensitive composition; (d) irradiating the image areas ofthe photosensitive composition to sufficient electron beam radiation tothereby increase the resistance of the photosensitive composition in theimage areas to an etchant.
 2. The process of claim 1 wherein the polymercomprises an olefin, an acrylate, a methacrylate, a norbornenecontaining polymer, an alicyclic polymer or combinations thereof.
 3. Theprocess of claim 1 wherein the polymer comprises a polyalkylacrylate ora polyalkylmethacrylate.
 4. The process of claim 1 wherein the polymerhas a molecular weight in the range of from about 1,000 to about800,000.
 5. The process of claim 1 wherein the photosensitive compoundcomprises an onium compound.
 6. The process of claim 1 wherein thephotosensitive compound comprises a sulfonium, iodonium or diazoniumcompound.
 7. The process of claim 1 wherein the substrate is selectedfrom the group consisting of silicon, aluminum, lithium niobate,polymeric resins, silicon dioxide, doped silicon dioxide, galliumarsenide, Group III/V compounds, silicon nitride, tantalum, copper,polysilicon, ceramics and aluminum/copper mixtures.
 8. The process ofclaim 1 wherein the exposing is conducted with an ArF laser.
 9. Theprocess of claim 1 wherein the exposing is conducted with an ArF laserat an exposure dose of from about 1 mJ/cm² to about 10 mJ/cm².
 10. Theprocess of claim 1 wherein the photosensitive composition furthercomprises one or more residual solvents selected from the groupconsisting of propylene glycol alkyl ether, butyl acetate, ethyleneglycol monoethyl ether acetate, diglyme, cyclopentanone and propyleneglycol methyl ether acetate.
 11. The process of claim 1 wherein saidpolymer is present in the photosensitive composition in an amount offrom about 50% to about 99%, and the photosensitive compound is presentin an amount of from about 1% to about 20% based on the weight of thenon-solvent parts of the photosensitive composition.
 12. The process ofclaim 1 wherein the photosensitive composition further comprises one ormore components selected from the group consisting of non-aromaticcolorants, dyes, anti-striation agents, leveling agents, crosslinkers,plasticizers, adhesion promoters, speed enhancers, solvents, dissolutioninhibitors, acid generators and surfactants.
 13. The process of claim 1wherein the developing is conducted with an aqueous alkaline solution.14. The process of claim 1 wherein the developing is conducted with ametal ion free aqueous alkaline solution.
 15. The process of claim 1wherein the developing is conducted with an aqueous alkaline solutioncomprising sodium hydroxide, potassium hydroxide, tetramethyl ammoniumhydroxide or mixtures thereof.
 16. The process of claim 1 wherein theelectron beam irradiating is conducted with a uniform, large-area,overall electron beam exposure source which simultaneously exposessubstantially all of the image areas of the photosensitive compositionsimultaneously.
 17. The process of claim 1 wherein the electron beamirradiating is conducted with a uniform large-area electron beam sourcewhich covers an exposure area of from about 4 square inches to about 256square inches simultaneously.
 18. The process of claim 1 wherein theelectron beam irradiating is conducted with a source which generates anelectron beam energy level ranging from about 0.5 to about 30 KeV. 19.The process of claim 1 wherein the electron beam irradiating is from asource which generates an electron dose ranging from about 1 to about500,000 μC/².
 20. The process of claim 1 wherein the electron beamirradiating is conducted from a source which generates an electron beamcurrent of from about 1 to about 150 mA.
 21. The process of claim 1wherein the electron beam irradiating is conducted while heating thesubstrate to a temperature of from about 20° C. to about 450° C.
 22. Theprocess of claim 1 wherein the electron beam irradiating is conducted ina gas selected from the group consisting of nitrogen, oxygen, hydrogen,argon, xenon, helium, ammonia, silane, a blend of hydrogen and nitrogen,ammonia and mixtures thereof.
 23. The process of claim 1 wherein theelectron beam irradiating is conducted while the substrate is under avacuum maintained in the range of from about 10⁻⁵ to about 10² torr. 24.The process of claim 1 further comprising the step of heating theimagewise exposed photosensitive composition prior to developing, for asufficient time and temperature to increase the rate at which the aciddecomposes the polymer in the imagewise exposed areas of thephotosensitive composition.
 25. A process for producing amicroelectronic device image which comprises: (a) coating and drying aphotosensitive composition onto a semiconductor substrate, whichphotosensitive composition comprises (i) at least one water insoluble,acid decomposable polymer which is substantially transparent toultraviolet radiation at a wavelength of about 193 nm, wherein saidpolymer is present in the photosensitive composition in an amountsufficient to form a uniform film of the composition components when itis coated on a substrate and dried; (ii) at least one photosensitivecompound capable of generating an acid upon exposure to sufficientactivating energy at a wavelength of about 193 nm, said photosensitivecompound being present in an amount sufficient to substantiallyuniformly photosensitize the photosensitive composition; (b) imagewiseexposing the photosensitive composition to sufficient activating energyat a wavelength of 193 nm to cause the photosensitive compound togenerate sufficient acid to decompose the polymer in the imagewiseexposed areas of the photosensitive composition; (c) developing thephotosensitive composition to thereby remove the exposed nonimage areasand leaving the unexposed image areas of the photosensitive composition;(d) irradiating the image areas of the photosensitive composition tosufficient electron beam radiation to thereby increase the resistance ofthe photosensitive composition in the image areas to an etchant.
 26. Theprocess of claim 25 further comprising the step of heating the imagewiseexposing the photosensitive composition prior to developing, for asufficient time and temperature to increase the rate at which the aciddecomposes the polymer in the imagewise exposed areas of thephotosensitive composition.
 27. A microelectronic device image producedby a process which comprises: (a) coating and drying a photosensitivecomposition onto a semiconductor substrate, which photosensitivecomposition comprises (i) at least one water insoluble, aciddecomposable polymer which is substantially transparent to ultravioletradiation at a wavelength of about 193 nm, wherein said polymer ispresent in the photosensitive composition in an amount sufficient toform a uniform film of the composition components when it is coated on asubstrate and dried; (ii) at least one photosensitive compound capableof generating an acid upon exposure to sufficient activating energy at awavelength of about 193 nm, said photosensitive compound being presentin an amount sufficient to substantially uniformly photosensitive thephotosensitive composition; (b) imagewise exposing the photosensitivecomposition to sufficient activating energy at a wavelength of 193 nm tocause the photosensitive compound to generate sufficient acid todecompose the polymer in the imagewise exposed areas of thephotosensitive composition; (c) developing the photosensitivecomposition to thereby remove the exposed nonimage areas and leaving theunexposed image areas of the photosensitive composition; (d) irradiatingthe image areas of the photosensitive composition to sufficient electronbeam radiation to thereby increase the resistance of the photosensitivecomposition in the image areas to an etchant.
 28. The microelectronicdevice image produced by the process of claim 27 which further comprisesthe step of heating the imagewise exposing the photosensitivecomposition prior to developing, for a sufficient time and temperatureto increase the rate at which the acid decomposes the polymer in theimagewise exposed areas of the photosensitive composition.